Scanning infrared radiation sensor

ABSTRACT

An infrared image is generated on an oscilloscope by sweeping a spot of short wavelength radiation across a P-N junction in doped germanium while applying voltage across a load resistor to the intensity modulation of an oscilloscope, the current passing through the load resistor being proportional to the intensity of infrared radiation incident on the P-type surface.

United States Patent Pruett l lMalCh 13, 1973 [54] SCANNING INFRAREDRADIATION 2,944,155 7/1960 Mayer ..3l3/65 A 2,99l,366 7/1961 Salzberg........307/88.5 SENSOR 3,040,205 6/1962 Walker ....3l3/65 A [75] Inventor:George R. Pruett, Richardson,TeX. 3,283,160 11/1968 Levitt et a1...307/88.5

290 .s [73] Assignee: The United States of America as lz/lg Cusdno at317/235 represented by the Secretary of the A W hi D PrimaryExaminerBenjamin A. Borchelt Assistant Examiner-H. A. Birmiel [22] Fled:1967 Attorney-Harry M. Saragovitz, Edward J. Kelly, Her- [21] App]. M619,138 bert Ber] and Aubrey J. Dunn [52] U.S.Cl. ..250/83.3 HP, 313/65AB, 3l5/l0, ABSTRACT 317/235 N An infrared image is generated on anoscilloscope by [5 Int- H011 sweeping a pot of hort wavelength radiationacross a Field 1; 317/235, 235 P-N junction in doped germanium whileapplying volt- 3 250/833 age across a load resistor to the intensitymodulation 833 211 0 of an oscilloscope, the current passing through theload resistor being proportional to the intensity of in- [56] ReferencesCited frared radiation incident on the P-type surface.

UNITED STATES PATENTS 4 Claims, I Drawing Figure 3,322.955 5/1967Desvignes 250 209 COO L AN T IR 2 SCANNING lMAGE DETECTOR BEAM SLABSOURCE 3,- 5 IR OPTICS R II1 T V V F OUTPUT PATENTEUHARI 3197s COOLANTSCANNING BEAM SOURCE Z DETECTOR SLAB IR OPTICS R OUTPUT! GeorgeR.Pruefl,

INVENTOR.

BY a

SCANNING INFRARED RADIATION SENSOR Various types of semiconductorinfrared detectors are known, such as those described on pages 89-106 ofthe book Infrared Methods" (Library of Congress Catalog Card No.60-8048) by Conn and Avery, printed in 1963 by the Academic Press of NewYork and London. None of these semiconductor infrared detectors producean output which could be used to generate a visible reproduction(scanned or otherwise) of an infrared image. Some types of infrareddetectors include image converters for producing visible images.Examples of such detectors are the metascopes, the Evapograph and theCondensograph, and the Barnes Far IR Camera. Another example is theSnooperscope, which uses a 1P25 image converter tube. All of theseexemplary infrared imaging devices suffer from one or more deficiencies,but mainly they are not readily adaptable for use as scanning detectors,the output of which could be used as a video signal. The most similardevice to the detector of the invention is the television vidicon pickuptube. However, the invention detector differs from a vidicon in that itmay employ a light beam in place of the electron beam of the vidicon,and in other ways that will be obvious from the following description.

An object of the invention is to provide a scanning type of infraredsensor.

Another object is to provide a novel infrared detector.

Yet another object is to provide a scanning type of infrared sensorwhich provides a video output signal.

These objects may be accomplished by the use of a three layersemiconductor detector having an infrared image formed on one of saidlayers and with a radiation beam scanning another of said layers toproduce a video output. In particular, the three layers are in the formof thin slabs of impurity doped germanium/with the first one of saidlayers being doped with a shallow acceptor type of substitutionalimpurity having an activation energy small compared to the thermalenergy at operating temperature, the second of said layers being dopedwith an impurity which forms an impurity photoconductor such as mercury,gold, or copper, and with the third layer being doped with asubstitutional donor impurity having an activation energy small comparedto the thermal energy at operating temperature. TI-Ie infrared image isformed on the first layer and the radiation beam is scanned on the thirdlayer. A voltage source is connected between said first and third layersand, through a series load resistor, provides a video voltage output.The radiation beam, in particular, is of a visible wavelength.

The invention may be best understood by reference to the single drawingfigure, which FIGURE is a schematic diagram of the invention.

Referring now to the drawing, reference numeral 1 designates an infraredoptics system, which may be any of the well known optical systemsuseable with infrared. This optics system forms an infrared image on onesurface of a detector slab 2. This slab consists of three thin layers,with a voltage source B connected to the two outer layers. The first ofsaid layers is designated by the numeral 3 and is germanium doped withan acceptor type of impurity, such as gallium. The second layer isgermanium doped with mercury, gold, or copper and is designated 4, andthe third layer is germanium doped with a donor type of impurity, suchas antimony and is designated 5. The resistivity of the second layer isin the range of megohm-centimeters at operating temperature. Alsoconnected in series with battery B is a resistor R, across which theoutput voltage for the sensor is taken. The variation of the current inthe circuit including said resistor causes variations in the voltagethereacross, and this varying voltage is the output voltage.

On the opposite side of detector slab 2 is a source of scanningradiation designated 6. This source produces a scanning beam (designatedby the dotted line 7) which scans slab 2 in a predetermined pattern,such as that pattern employed in television pickup tubes, e.g., a numberof spaced parallel lines. As the scanning beam traverses layer 5 of slab2, a voltage is developed across resistor R in accord with the infraredimage on layer 3 of slab 2.

The manner of operation of slab 2 is as follows: the infrared image fromthe infrared optics l is focused on layer 3 of slab 2 and penetrates it(layer 3) uniformly. Majority carriers (holes) are generated in the bulkof layer 4 by the infrared image. The scanning beam 7 on layer 5 of slab2 may be in the form of visible light. Said beam generates hole-electronpairs. Minority carriers (holes) diffuse through the barrier establishedby the P- N junction between layers 4 and 5 with no loss in potential.Majority carriers (electrons) are blocked by the P-N junction. Thebattery B is connected to the layers 3 and 5 by ring contacts to assuregood electrical contact. Layer 3 of slab 2 should have as high aconductivity as possible without absorbing or scattering the infraredsignal image. The slab 2 is provided with a coolant such as 8 tomaintain the low temperature required. This coolant may be, for example,liquid nitrogen in the case. of gold-doped germanium, liquid neon in thecase of mercury-doped germanium, and liquid hydrogen in the case ofcopper-doped germanium. Liquid helium, of course, would be a suitablecoolant for all types of germanium. The P-N junction established betweenlayer 4 and layer 5 blocks the current that would normally flow betweencontacts fixed on layers 3 and 5 through the external circuit includingresistor R and battery B, except when illuminated by scanning beam 7.The scanning beam generates a current path through layer 5, or, acts asa selective switch. The scanning beam can consist of any energy beamgreater than the energy gap of germanium, i.e., it must generatehole-electron pairs at the surface of layer 5 rather than in the bulk.Infrared should be filtered from this scanning beam. Ultravioletwavelengths would be usable. The means for generating the scanning beammay take only one of several well known forms, such as a cathode raytube flying spot scanner with suitable optics. The scanning beam couldalso be a beam of electrons, but a suitable vacuum enclosure would berequired.

While a specific embodiment of the invention has been described, otherembodiments may be obvious to one skilled in the art, in light of theinstant disclosure. While the infrared optics l of the drawing has beenshown as a double convex refracting lens, other suitable opticalelements may be employed, either reflecting or refracting. Also, otherelements, e.g. cadmium or zinc may be used as impurities in layer 4 ofslab 2.

I claim:

1. A radiation sensor including: a radiation detector comprising first,second, and third continuous semiconductor layers, said first layerbeing infrared transparent, said second layer being a high resistivityimpurity photoconductor contacting said first layer, said third layerbeing a material of opposite conductivity type from said second layer,and making a broad area contact to form a photodiode with said secondlayer, bias means connected to said detector, means for directingradiation on said first layer of said detector, means for scanning saidthird layer of said detector with an energy beam capable of generatinghole-electron pairs from to said bias means.

2. The sensor of claim 1 wherein said semiconductor is germanium.

3. The sensor of claim 1 or 2 wherein said first layer is germaniumdoped with an acceptor impurity with an activation energy small comparedto the thermal energy at operating temperature.

4. The sensor of claim 1 or 2 wherein said third layer is germaniumdoped with a donor impurity with an activation energy small compared tothe thermal energy at operating temperature.

1. A radiation sensor including: a radiation detector comprising first,second, and third continuous semiconductor layers, said first layerbeing infrared transparent, said second layer being a high resistivityimpurity photoconductor contacting said first layer, said third layerbeing a material of opposite conductivity type from said second layer,and making a broad area contact to form a photodiode with said secondlayer, bias means connected to said detector, means for directingradiation on said first layer of said detector, means for scanning saidthird layer of said detector with an energy beam capable of generatinghole-electron pairs from the surface of said layer, and output meansconnected to said bias means.
 1. A radiation sensor including: aradiation detector comprising first, second, and third continuoussemiconductor layers, said first layer being infrared transparent, saidsecond layer being a high resistivity impurity photoconductor contactingsaid first layer, said third layer being a material of oppositeconductivity type from said second layer, and making a broad areacontact to form a photodiode with said second layer, bias meansconnected to said detector, means for directing radiation on said firstlayer of said detector, means for scanning said third layer of saiddetector with an energy beam capable of generating hole-electron pairsfrom the surface of said layer, and output means connected to said biasmeans.
 2. The sensor of claim 1 wherein said semiconductor is germanium.3. The sensor of claim 1 or 2 wherein said first layer is germaniumdoped with an acceptor impurity with an activation energy small comparedto the thermal energy at operating temperature.